In a Long Term Evolution (Long Term Evolution, LTE) system, to support a hybrid automatic repeat request (Hybrid Automatic Repeat Request, HARQ), user equipment needs to feed back a hybrid automatic repeat request-acknowledgement (HARQ Acknowledgment, HARQ-ACK) corresponding to a physical downlink shared channel (Physical Downlink Shared Channel, PDSCH) to a base station by using a physical uplink control channel (Physical Uplink Control Channel, PUCCH) or a physical uplink shared channel (Physical Uplink Shared Channel, PUSCH). The HARQ-ACK may be referred to as an acknowledgement (Acknowledgment, ACK) or a negative acknowledgement (Negative Acknowledgement, NACK). The user equipment needs to receive, by using a physical hybrid automatic repeat request indicator channel (Physical HARQ Indicator Channel, PHICH), a HARQ-ACK corresponding to the PUSCH.
An existing LTE system includes two types of frame structures. A first type of frame structure is used for frequency division duplex (Frequency-Division Duplex, FDD), and a second type of frame structure is used for time division duplex (Time-Division Duplex, TDD). A length of each subframe in the two types of frame structures is 1 ms.
Uplink-downlink timing indicates that if the user equipment feeds back information (usually feeds back the ACK or the NACK) in an nth uplink subframe, to indicate whether the user equipment correctly decodes downlink data corresponding to an (n−k)th downlink subframe, the uplink-downlink timing is k subframes, and may also be referred to as a timing length.
In LTE, for different uplink-downlink subframe configuration ratios, TDD has different uplink-downlink timing for each configuration ratio. Due to this complex timing relationship, protocol design is more complex, and it cannot be ensured that services have a uniform latency on an air interface.